Sheryl Crow has been interviewed by officials as part of the long-running Lance Armstrong doping investigation, it has been revealed.

The superstar singer was roped in to the scandal last year, when she provided information to federal agents as they were preparing a case against the seven-time Tour de France champion.

Mr Armstrong was stripped of his titles last month after he announced he would stop fighting accusations that he used illegal techniques over the course of his career.

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Couple: But Sheryl Crow agreed to talk to officials investigating Lance Armstrong's doping last year

Joy: The pair were together from 2003 to 2006, and became engaged before breaking up

Ms Crow, who dated the sportsman from 2003 to 2006 and was engaged to marry him before their break-up, helped agents with their inquiries in late 2011, according to the Daily News.

The officials were working on a case which was set to go before a grand jury, though no charges were ever filed.

Anti-doping authorities announced a new probe into Mr Armstrong's past in June, and two months later the cyclist decided he would no longer contest the charges.

It is not known what Ms Crow told the officials who interviewed her, and representatives have refused to comment on the contents of the investigation.

Close: Despite their split, the singer and the cyclist are believed to get on well together

Glamor: Armstrong was briefly engaged to singer Sheryl Crow before he ended their three-year relationship -- one of several celebrities he was romantically linked with

The musician has previously commented on the doping allegations in a 2005 interview with USA Today, at a time when she was still engaged to Mr Armstrong.

She dismissed rumours that the accusations were the result of anti-Americanism from French fans, saying: 'I don't think the French people are on a mission to strip him of his integrity.

'It's just a handful of people pursuing that theory, and it's tiresome and a nuisance, and it will eventually end, I hope.'

The former couple are said to be still on good terms with one another.

When they were together, Ms Crow spent time with Mr Armstrong in places such as hotels and private jets which were, according to the cyclist's teammates, focal points of illegal doping networks.

Done: Lance Armstrong's decision was viewed as an admission of guilt by the US Anti-Doping Agency

Banned: Armstrong has been stripped of his seven titles and can no longer race in a sport that he made famous. Millions of Americans were drawn to cycling because of Armstrong's dominance

Last week's fateful announcement from the US Anti-Doping Agency effectively destroyed his legacy as one of the greatest cyclists in history and rubs a black smudge on a story that inspired millions of fans, drawn to his story of returning to glory after recovering from horrific cancer.

The USADA acted within an hour of Armstrong's announcement that he would stop fighting charges that he used blood doping to illegitimately enhance his performance.

Despite the action, Armstrong maintains his innocence and called the USADA's case a 'witch hunt.'

40-year-old Armstrong, who retired a year ago, is now officially a drug cheat in the eyes of his nation's doping agency.

USADA chief executive Travis Tygart said earlier that the agency has the authority to remove the titles from the 40-year-old athlete - and would act promptly to do so.

Comeback: Armstrong was given a 40 percent chance of survival after he was diagnosed with testicular cancer

'Innocent': Armstrong still claims he did not use performance enhancing drugs and says the charges against him are 'unconstitutional'

Armstrong argued that only the International Cycling Union, which oversees the Tour de France, has that power.

'USADA cannot assert control of a professional international sport and attempt to strip my seven Tour de France titles,' he said in a statement. 'I know who won those seven Tours, my teammates know who won those seven Tours, and everyone I competed against knows who won those seven Tours.'

USADA maintains that Armstrong has used banned substances as far back as 1996, including the blood-booster EPO and steroids as well as blood transfusions -- all to boost his performance.

'It is a sad day for all of us who love sport and athletes,' Mr Tygart said. 'It's a heartbreaking example of win at all costs overtaking the fair and safe option. There's no success in cheating to win.'

Armstrong declined to enter arbitration - his last option - because he said he was weary of fighting accusations that have dogged him for years. He has consistently pointed to the hundreds of drug tests that he has passed as proof he was clean.

'There comes a point in every man's life when he has to say, "Enough is enough." For me, that time is now,' Armstrong said. He called the USADA investigation an 'unconstitutional witch hunt.'

'I have been dealing with claims that I cheated and had an unfair advantage in winning my seven Tours since 1999,' he said. 'The toll this has taken on my family and my work for our foundation and on me leads me to where I am today -- finished with this nonsense.'

Family: Lance Armstrong had a fourth child, Max, in 2010 with his girlfriend Anna Hansen, even though he thought he was sterile because of the cancer

Father: Armstrong has a son Luke and twin girls Isabelle and Grace with his ex-wife

Armstrong's disgrace marks the dizzying fall of an athlete who was regarded as a hero by millions because of his remarkable recovery from testicular cancer.

His foundation has raised some $500million through the sale of iconic 'Livestrong' bracelets, which were seemingly ubiquitous during Armstrong's heyday.

Although he had already been crowned a world champion and won individual stages at the Tour de France, Armstrong was still relatively unknown in the US until he won the epic race for the first time in 1999.

It was the ultimate comeback tale: When diagnosed with cancer, doctors had given him less than a 50 percent chance of survival before surgery and brutal cycles of chemotherapy saved his life.

He was diagnosed with cancer in October 1996 and surgeons removed a tumor-ridden testicle during an emergency operation, though the tumors had spread to his lungs, abdomen and brain.

Over the course of two months, he underwent extensive chemotherapy and surgery to combat the cancer.

By January 1998 -- one year after his chemotherapy ended -- he was back on the bike and aggressively training.

Before his cancer, he had won several stages of the Tour de France in past years, but he attacked the race aggressively - with new passion.

He forged a reputation for himself as a brutal competitor, forcing himself through grueling offseason workouts no one else could match, then crushing his rivals in the Alps and the Pyrenees during the Tour.

Champion: Armstrong developed worldwide recognition as a brutal competitor -- crushing the competition for seven years running

Grueling: Armstrong was known for horrific off-season workouts that were nearly unmatched by his competitors

His comeback began in September 1998, when he came in fourth at the Vuelta a España - one of cycling's three Grand Tours.

In 1999, he won the Tour de France and then continued winning it each of the next six years - capturing the attention of Americans.

Cycling suddenly became popular and the week-long Tour was broadcast on American TV in its entirety.

Armstrong's riveting victories, his work for cancer awareness and his gossip-page romances with Sheryl Crow, fashion designer Tory Burch and actress Kate Hudson made him a figure who transcended sports.

His dominance of the Tour de France elevated the sport's popularity in America to unprecedented levels. His story and success enabled him to enlist lawmakers and global policymakers to promote cancer awareness and research. His Lance Armstrong Foundation has raised nearly $500 million since its founding in 1997.

Armstrong walked away from the sport in 2011 without being charged following a two-year federal criminal investigation into many of the same accusations he faces from USADA.

The federal probe was closed in February, but USADA announced in June it had evidence Armstrong used banned substances and methods - and encouraged their use by teammates. The agency also said it had blood tests from 2009 and 2010 that were 'fully consistent' with blood doping.

Included in USADA's evidence were emails written by Armstrong's former US Postal Service teammate Floyd Landis, who was stripped of his 2006 Tour de France title after a positive drug test. Landis' emails to a USA Cycling official detailed allegations of a complex doping program on the team.

USADA also said it had 10 former Armstrong teammates ready to testify against him. Other than suggesting they include Landis and Tyler Hamilton, both of whom have admitted to doping offenses, the agency has refused to say who they are or specifically what they would say.

Extraordinary: Armstrong's seven straight Tour de France titles led to a surge in the interest in cycling in America and made him a sports icon

Turning: Former teammate Tyler Hamilton accused Armstrong of blood doping and said he had encouraged other members of his cycling team to dope, as well

'There is zero physical evidence to support (the) outlandish and heinous claims. The only physical evidence here is the hundreds of (doping) controls I have passed with flying colors,' Armstrong said before the ruling.

Armstrong sued USADA in Austin, where he lives, in an attempt to block the case and was supported by the UCI, the sport's governing body. A judge threw out the case on Monday, siding with USADA despite questioning the agency's pursuit of Armstrong in his retirement.

'USADA's conduct raises serious questions about whether its real interest in charging Armstrong is to combat doping, or if it is acting according to less noble motives,' such as politics or publicity, US District Judge Sam Sparks wrote.

Now the ultra-competitive Armstrong has done something virtually unthinkable for him: He has quit before a fight is over.

'Today I turn the page. I will no longer address this issue, regardless of the circumstances. I will commit myself to the work I began before ever winning a single Tour de France title: serving people and families affected by cancer, especially those in underserved communities,' Armstrong said.

Armstrong could have pressed his innocence in USADA's arbitration process, but the cyclist has said he believes most people have already made up their minds about whether he's a fraud or a persecuted hero.

Hot water: Armstrong has faces questions about drug use and doping since the 1990s

Created in 2000, USADA is recognized by Congress as the official anti-doping agency for Olympic sports in the United States. Its investigators joined US agents during the federal probe, Mr Tygart, the head of USADA had dismissed Armstrong's lawsuit as an attempt at 'concealing the truth.' He said the agency is motivated by one goal -- exposing cheaters in sport.

Others close to Armstrong were caught up in the charges: Johan Bruyneel, the coach of Armstrong's teams, and three members of the medical staff and a consultant were also charged. Bruyneel is taking his case to arbitration, while two medical team staffers and consulting doctor Michele Ferrari didn't formally contest the charges and were issued lifetime ban by USADA. Ferrari later said he was innocent.

In a sport rife with cheaters, Armstrong has been under constant suspicion since the 1990s from those who refused to believe he was a clean rider winning cycling's premier event against a field of doped-up competition.

He had tense public disputes with USADA, the World Anti-Doping Agency, some former teammates and assistants and even Greg LeMond, the first American to win the Tour de France.

Through it all, Armstrong vigorously denied any and all hints, rumors and direct accusations he was cheating. He had the blazing personality, celebrity and personal wealth needed to fight back with legal and public relations battles to clear his name - and he did, time after time.

Armstrong won his first Tour at a time when doping scandals had rocked the race. He was leading the race when a trace amount of a banned anti-inflammatory corticosteroid was found in his urine; cycling officials said he was authorized to use a small amount of a cream to treat saddle sores.

Rally: Less than three years after his cancer diagnosis, Armstrong won his first Tour de France

After Armstrong's second victory in 2000, French judicial officials investigated his Postal Service team for drug use. That investigation ended with no charges, but the allegations kept coming.

Armstrong was criticized for his relationship with Ferrari, who was banned by Italian authorities over doping charges in 2002. Former personal and team assistants accused Armstrong of having steroids in an apartment in Spain and disposing of syringes that were used for injections.

In 2004, a Dallas-based promotions company initially refused to pay him a $5 million bonus for winning his sixth Tour de France because it wanted to investigate allegations raised by media in Europe. Testimony in that case included former teammate Frankie Andreu and his wife, Betsy, saying Armstrong told doctors during his 1996 cancer treatments that he had taken a cornucopia of steroids and performance-enhancing drugs.

Two books published in Europe, 'LA Confidential' and 'LA Official,' also raised doping allegations and, in 2005, French magazine L'Equipe reported that retested urine samples from the 1999 Tour showed EPO use.

Armstrong fought every accusation with denials and, in some cases, lawsuits against the European media outlets that reported them.

But he showed signs that he was tiring of the never-ending questions. Armstrong retired (for the first time) in 2005 and almost immediately considered a comeback before deciding to stay on the sidelines, in part, because he didn't want to keep answering doping questions.

Seven titles: These are the seven Tour de France victories that Lance Armstrong achieved -- more than any other racer in history

'I'm sick of this,' Armstrong said in 2005. 'Sitting here today, dealing with all this stuff again, knowing if I were to go back, there's no way I could get a fair shake - -on the roadside, in doping control, or the labs.'

But three years later, Armstrong was 36 and itching to ride again. He came back to finish third in the 2009 Tour de France.

Armstrong raced in the Tour again in 2010, under the cloud of the federal criminal investigation. Early last year, he quit the sport for good, but made a brief return as a triathlete until the USADA investigation shut him down.

During his sworn testimony in the dispute over the $5 million bonus, Armstrong said he wouldn't take performance enhancing drugs because he had too much to lose.

'(The) faith of all the cancer survivors around the world. Everything I do off the bike would go away, too,' Armstrong said then.

'And don't think for a second I don't understand that. It's not about money for me. Everything. It's also about the faith that people have put in me over the years. So all of that would be erased.'

VIDEO: 'I am not going to be distracted from this fight'. Armstrong spoke in Montreal on Aug 31, after recieving a lifetime ban from cycling